The present invention relates generally to formed optical filters, i.e. optical lenses and panels that are injection molded, extruded or cast. More specifically, the present invention relates to molded optical filters containing organic dyes that provide high optical density filtering characteristics across a narrowly selected infra-red wavelength range of between about 710 nm-1500 nm, while greatly improving visible light transmission across the remaining visible light spectrum.
In a number of fields that use lasers, there is a growing awareness that certain wavelengths of energy emissions are harmful to the eye. For example, energy emitted from lasers can cause both temporary and permanent blindness, and can be disorienting to those people that have been exposed. As applications that utilize such energy emissions are more frequently employed, the adverse effects of energy emissions utilized in these developing technologies are becoming more fully recognized. For example, there are a number of optical communication protocols that utilize infrared and near infrared energy emissions. Further, such systems often employ cohesive light emissions in the form of lasers for the transmission of data. Similarly, there are a number of military applications that employ infra-red and near infra-red laser energy emissions in connection with the sighting of weapons and target acquisition. As the environments in which the use of such energy emissions expand, the potential for accidental exposure to such emissions also greatly increases.
In the past, to avoid accidental exposure to infrared and/or laser emissions, people have attempted to protect their eyes through the use of panels, lenses and goggles having broad bandwidth, via non-selective dyes included in the transparent matrix material. These broad wavelength filters screen out both the harmful IR wavelengths and much of the surrounding wavelengths, thus reducing the potential for exposure to harmful emission levels. In this regard, the non-selective filters do in fact reduce the magnitude of the exposure by screening out the targeted harmful wavelengths of energy.
The problem with the prior art approach is that the broad bandwidth non-selective filters also significantly block many of the visible light wavelengths, lowering the visible light transmission (VLT) through the lens or panel and adversely impacting the visual acuity of the wearer. These broad wavelength shields imposed severe limitations on the visibility of the wearer even in broad daylight. This problem becomes further pronounced as available light levels in the ambient environment are decreased. The reduction in available visible light significantly impacts the wearer's ability to carry out certain functions, impairs their depth perception, and impairs their ability to perceive certain colors.
Another difficulty encountered in the prior art is compatibility of the filtering materials with the matrix material, i.e. glass or plastic. Glass and high impact polymers, such as polycarbonate, both require that the additives used to modify the transmissivity be chemically and thermally compatible with the high temperatures required in making or processing of the material. The range of substances that are available that are both compatible with high processing temperatures and capable of imparting the desired filtering properties is very narrow.
An example of the performance characteristics of a prior art IR filter is illustrated in the graphs at FIGS. 1a and 1b. FIG. 1 illustrates the filtering characteristics of a prior art optical filter, in terms of optical density, wherein the filter is tailored for filtering energy in the range around 810 nm. As can be seen, the prior art filter provides a filtering performance curve that exhibits a full width, 90 nm, filtering notch at half the maximum 11 optical density (OD) filtering characteristic of the lens. In other words, the lens exhibits a full-width half max (FWHM) value of 90 nm, meaning that the filter exhibits a 90 nm filtering notch at an optical density of 5.5 (½ the maximum OD of 11). Turning to FIG. 1b, the performance of the same filter described above is displayed in terms of light transmission. It can be seen that the prior art filter having a FWHM of 90 nm, blocks nearly 100% of the energy between 730 nm and 870 nm. Further, the prior art filter exhibits a visible light transmission (VLT) across the remaining spectrum of only around 40-45%. As can be seen, the results indicate a relatively low performance filter with a limited VLT value.
Another alternative for manufacturing a protective filter or lens was to provide a coating on an outer surface of a lens after it was formed. The difficulty is that such coating processes dramatically increase the cost of the lenses. Further, coated lenses often require special handling of the finished product since the coatings are fragile and tend to scratch easily and must be compensated due to dependence upon the angle of the incident energy.
Accordingly, while interference coated filters and lenses with selective transmission properties do exist, they are usually quite costly, and fail to provide the advantages of this invention as to low cost, and to versatility, breadth of function and beneficial effect.
There is thus a real need in the industry for a selective wavelength filter that blocks a narrow band of energy emissions centered on a desired filtering frequency and that also preserves a relatively high visible light transmission (VLT). There is a further need for a selective wavelength filter panel, lens or shield that is processed from a polymer matrix and that includes an organic dye or dyes therein for filtering out energy emissions in a narrow frequency band having a FWHM value of 44 nm or less while preserving high levels of visible light transmission. Finally, there is a need for a method of producing a polymer lens filter that includes an organic dye or dyes therein that is suitable for filtering a narrow frequency band having a FWHM value of 44 nm or less.